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<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
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<body>
    <body>
    <script>

    var r = 3;
    var perimeter = 2 * Math.PI * r;
    console.log("圆的周长是：" + perimeter);

    </script>
</body>

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